From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6027AC433B4 for ; Thu, 8 Apr 2021 17:50:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2026C61139 for ; Thu, 8 Apr 2021 17:50:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232144AbhDHRuy (ORCPT ); Thu, 8 Apr 2021 13:50:54 -0400 Received: from mga11.intel.com ([192.55.52.93]:40693 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232086AbhDHRux (ORCPT ); Thu, 8 Apr 2021 13:50:53 -0400 IronPort-SDR: 9192zSNf1+v5XkiV3m4u4iznRpo+nYKI0EV9jPEpLL6u+xdVu9MSvjrkPzGfjN4zQUjBqkbk0C r6vWdfaO1T8g== X-IronPort-AV: E=McAfee;i="6000,8403,9948"; a="190398903" X-IronPort-AV: E=Sophos;i="5.82,207,1613462400"; d="scan'208";a="190398903" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Apr 2021 10:50:42 -0700 IronPort-SDR: p3wh+dLx0XeI3dTL4S60AIwO/HXvhpohRVDWptGhIxxc+i8Sq6es+WRDGpb/HfdaG4cxlzj3zl OHfGZJhhjuhg== X-IronPort-AV: E=Sophos;i="5.82,207,1613462400"; d="scan'208";a="530687284" Received: from yoojae-mobl.amr.corp.intel.com (HELO [10.251.26.54]) ([10.251.26.54]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Apr 2021 10:50:41 -0700 Subject: Re: [PATCH v4 1/4] dt-bindings: i2c: aspeed: add transfer mode support From: Jae Hyun Yoo To: Rob Herring Cc: Mark Rutland , devicetree@vger.kernel.org, linux-aspeed , Wolfram Sang , Andrew Jeffery , OpenBMC Maillist , Brendan Higgins , Linux I2C , Tao Ren , Cedric Le Goater References: <20210224191720.7724-1-jae.hyun.yoo@linux.intel.com> <20210224191720.7724-2-jae.hyun.yoo@linux.intel.com> <20210306203011.GA1152769@robh.at.kernel.org> Message-ID: Date: Thu, 8 Apr 2021 10:50:41 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org Ping. On 3/10/2021 7:55 AM, Jae Hyun Yoo wrote: > On 3/9/2021 6:15 PM, Rob Herring wrote: >> On Tue, Mar 9, 2021 at 10:02 AM Jae Hyun Yoo >> wrote: >>> >>> Hi Rob, >>> >>> On 3/6/2021 12:30 PM, Rob Herring wrote: >>>> On Wed, Feb 24, 2021 at 11:17:17AM -0800, Jae Hyun Yoo wrote: >>>>> Append bindings to support transfer mode. >>>>> >>>>> Signed-off-by: Jae Hyun Yoo >>>>> Reviewed-by: Brendan Higgins >>>>> --- >>>>> Changes since v3: >>>>> - None >>>>> >>>>> Changes since v2: >>>>> - Moved SRAM resources back to default dtsi and added mode selection >>>>>     property. >>>>> >>>>> Changes since v1: >>>>> - Removed buffer reg settings from default device tree and added >>>>> the settings >>>>>     into here to show the predefined buffer range per each bus. >>>>> >>>>>    .../devicetree/bindings/i2c/i2c-aspeed.txt    | 37 >>>>> +++++++++++++++---- >>>>>    1 file changed, 30 insertions(+), 7 deletions(-) >>>>> >>>>> diff --git a/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt >>>>> b/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt >>>>> index b47f6ccb196a..242343177324 100644 >>>>> --- a/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt >>>>> +++ b/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt >>>>> @@ -17,6 +17,20 @@ Optional Properties: >>>>>    - bus-frequency    : frequency of the bus clock in Hz defaults >>>>> to 100 kHz when not >>>>>                 specified >>>>>    - multi-master     : states that there is another master active >>>>> on this bus. >>>>> +- aspeed,i2c-xfer-mode      : should be "byte", "buf" or "dma" to >>>>> select transfer >>>>> +                      mode defaults to "byte" mode when not >>>>> specified. >>>>> + >>>>> +                      I2C DMA mode on AST2500 has these restrictions: >>>>> +                        - If one of these controllers is enabled >>>>> +                            * UHCI host controller >>>>> +                            * MCTP controller >>>>> +                          I2C has to use buffer mode or byte mode >>>>> instead >>>>> +                          since these controllers run only in DMA >>>>> mode and >>>>> +                          I2C is sharing the same DMA H/W with them. >>>>> +                        - If one of these controllers uses DMA >>>>> mode, I2C >>>>> +                          can't use DMA mode >>>>> +                            * SD/eMMC >>>>> +                            * Port80 snoop >>>> >>>> How does one decide between byte or buf mode? >>> >>> If a given system makes just one byte r/w transactions most of the time >>> then byte mode will be a right setting. Otherwise, buf mode is more >>> efficient because it doesn't generate a bunch of interrupts on every >>> byte handling. >> >> Then why doesn't the driver do byte transactions when it gets small >> 1-4? byte transactions and buffer transactions when it gets larger >> sized transactions. > > Good question and it could be an option of this implementation. > Actually, each mode needs different register handling so we need to add > additional conditional branches to make it dynamic mode change depends > on the data size which can be a downside. Also, checked that small > amount of data transfer efficiency in 'buf' transfer mode is almost same > to 'byte' mode so there would be no big benefit from the dynamic mode > change. Of course, we can remove the 'byte' transfer mode but we should > also provide flexibility of configuration on what this hardware can > support, IMO. > > Thanks, > Jae